"Adobe announced at the Web 2.0 conference on Tuesday that it was donating the scripting language engine from Flash to the Mozilla Foundation, where it will become an open source project called Tamarin as well as being integrated directly into the Firefox Web browser.

Specifically, Adobe is opening up its ActionScript Virtual Machine, which forms the core of Flash Player version 9. The most recent release in June added improved debugging, faster start times, full runtime error reporting, and better performance.
The code is the largest contribution to Mozilla since the organization was founded in 2003."